Jan 30, 2009
By Michael Mecham
NASA is in final preparations to launch the 897-pound Orbiting Carbon Observatory (OCO) into the so-called “A-Train” of other climate monitoring satellites in an effort to pinpoint where carbon dioxide is being emitted and absorbed.
The answer to that balancing act should help define how much man is contributing – and in what ways – to greenhouse gases such as carbon dioxide (CO2) that are believed to be greatly altering global climate.
Built by Orbital Sciences Corp. (OSC) of Dulles, Va., OCO carries a single instrument that includes three high-resolution grating spectrometers from Hamilton Sundstrand Sensor Systems of Pomona, Calif., and is to be launched on an OSC Taurus XL 3110 from Vandenberg Air Force Base, Calif., on Feb. 23.
The three-stage booster will use a direct insertion to put it in a 705-kilometer (438-mile) high near-polar, sun-synchronous orbit. It will circle the Earth every 99 minutes and repeat the same ground track every 16 days.
OCO is pegged as a two-year “exploratory” mission and has a lifecycle cost of $278 million, including the spacecraft, launch and operations. Once in place, it will lead a flotilla of atmospheric Earth observatories already in the same orbit from NASA and the European Space Agency. The “Afternoon,” or “A-Train” constellation includes Aqua, CloudSat, Parasol, Calipso and Aura.
OCO is to be installed at the head of the pack and its findings will be closely correlated with data gathered by the other spacecraft, particularly NASA’s Aqua, which is primarily studying oceans and sea ice, and Aura, which is focused on atmospheric studies, explained OCO Program Executive Eric Ianson of NASA headquarters.
Findings also will be coordinated with the Japanese GOSAT mission, which is using a different instrument pack that also is providing CO2 counts (Aerospace DAILY, Jan. 26). Correlations also will be made with aircraft CO2 survey flights and ground-station monitors.
Scientists have been mapping CO2 levels in the lower atmosphere for years, explained Anna Michalak, an OCO science team member from the University of Michigan/Ann Arbor. The problem is that these surveys offer only a limited snapshot of what’s going on globally. OCO is the first spacecraft with a sole mission to produce a global CO2 survey.
Its spectrometer doesn’t actually measure CO2. Instead, it makes calibrations from sunlight reflections of molecules in the atmosphere, from which scientists can deduce CO2 concentration levels. To do this, the instrument will be periodically repositioned to obtain readings from different angles – both straight down “nadir” and angled “glint” samples.
Even with concern about how much man’s activities are building up carbon dioxide levels, the actual population of CO2 varies across the globe and has been difficult to track. How much it varies is one of the big question marks.
Equally difficult is knowing the location, timing and quantity of CO2 that is naturally produced and its location versus what man’s activities emit. The OCO mission is designed to fill in those gaps.
Artist’s concept of OCO: NASA